fix: Try to fix #82 (#91)

Co-authored-by: Samuel Mutel <[email protected]>

Add several options for RestAPI (#93)

Co-authored-by: Samuel Mutel <[email protected]>

Fix: Add dependencies for psycopg2 and setuptools python (#90)

Allow variables overwrite from group_vars/host_vars (#83)

The current implementation is loading variables from vars/ directory
when the role is evaluated. Doing so prevent user to overwrite them in
their group_vars/host_vars. A user can have several patroni clusters
targeted by the same playbook, example:

```yaml
- name: Configure PostgreSQL
  hosts: role_patroni_server
  any_errors_fatal: true
  become: true
  become_user: root
  roles:
    - kostiantyn-nemchenko.patroni
```

This PR follow the same implementation used by Jeff Geerling in each of
its roles (kudos to him).